When in solution, lactose exists in equilibrium between two isomeric forms: α-lactose and β-lactose. α-lactose is the desired form. The solubility of lactose (in either form) decreases as the temperature is lowered.
Crystallisation of a lactose solution produces crystals of α-lactose monohydrate (ALM). As ALM crystals are formed β-lactose coverts to α-lactose in the solution to maintain the equilibrium between these two isomers.
The aim of a crystallisation process is to produce                crystals in high yield, and        high purity.        
Methods for making lactose have been reported, such as in U.S. Pat. No. 4,404,038. Such methods suffer from one or more technical limitations such as the quality of the input, depositions and hygiene, viscosity, heat transfer efficiency, quality of crystallisation and particle size distribution, and loss of fines, leading to low efficiency and yield (see Chapter 4 of Advanced Dairy Chemistry, volume 3 [ed. McSweeney and Fox, Springer Science, 2009]).
In this specification, where reference has been made to external sources of information, including patent specifications and other documents, this is generally for the purpose of providing a context for discussing the features of the present invention. Unless stated otherwise, reference to such sources of information is not to be construed, in any jurisdiction, as an admission that such sources of information are prior art or form part of the common general knowledge in the art.
It is an object of the present invention to provide a method of producing lactose which at least provides the public with a useful choice.
Other objects of the invention may become apparent from the following description which is given by way of example only.